Epithelial tumors of the intestines are a major cause of morbidity and mortality worldwide. The colon (including the rectum) is host to more primary neoplasms than any other organ in the body. Colorectal cancer ranks second only to bronchogenic carcinoma among the cancer killers. Adenocarcinomas constitute the vast majority of colorectal cancers and represent 70% of all malignacies arising in the gastrointestinal tract. The small intestine is an uncommon site for benign or malignant tumors despite its great length and vast pool of dividing mucosal cells. The classification of intestinal tumors is the same for the small intestine and colon. Although small intestinal tumors are addressed first, the bulk of the discussion is devoted to colorectal neoplasia.

Tumors of the small intestine

Although the small bowel represents 75% of the length of the alimentary tract, its tumors account for only 3 to 6% of gastrointestinal tumors, with a slight preponderance of benign tumors. The most frequent benign tumors in the small intestine are adenomas and smooth muscle tumors. Lipomas, angiomas, and rare hamartomatous mucosal lesions constitute the remainder. One of the enigmas of medicine is the rarity of malignant tumors of the small intestine annual US death rate is under 1000, representing only about 1% gastrointestinal malignancies. Small intestinal adenocarcinomas and carcinoids have roughly equal incidence followed in order by lymphomas and sarcomas. Because the latter three exhibit a broader distrubution than the small intestine.

Adenomas

Adenomas account for approximately 25% of benign small intestinal tumors with benign stromal tumors (leiomyomas), lipomas , and neuromatous lesions following in frequency. Most adenomas occur in the region of the ampulla of vater. Patients usually present between the ages of 30 to 60 with occult blood loss and rarely with obstruction or intrussusception; some are discovered incidentally during radiographic investigation. Patients with familial polyposis coli are particularly prone to developing periampullary adenomas. Macroscopically these adenomas resemble their counterparts in the colon. Frequently there is extension of adenomatous tissue into the ampullary orifice rendering surgical excision difficult sort of a pancreatoduodenectomy to remove the entire ampullary region.

Adenocarcinoma

The large majority of small intestinal adenocarcinomas occur in the duodenum and jejunum. With a presenting age usually between 40 and 70years of age. These tumors grow in a napkin ring encircling pattern or as polypoid fungating masses in a manner similar to colonic cancers. Tumors in the duodenum, particularly involving the ampulla of Vater, may present with obstructive jaundice early in their course. More typically cramping pain, nausea, vomiting and weight loss are the presenting signs and symptoms, resulting from intestinal obstruction. As with adenomas, fatigue from occult blood loss may be the only wign. Rarely the tumorous mass is a lead point for intussusception.

At the time of diagnosis, most tumors have already penetrated the bowel wall invaded the mesentery or other segments of the gut spread to regional nodes, and some times metastasized to the liver and more widely by the time of diagnosis. Despite these problems, wide en bloc excision of these cancers yields about a 70% 5 year survival rate.